ABSTRACT Wet age-related macular degeneration (AMD) is a leading cause of vision loss in old patients. In wet AMD, excessive vascular endothelial growth factor (VEGF) causes abnormal angiogenesis and vascular leakage, which in turn damages the retina. The overall goal of this proposal is to determine the mechanism how excessive VEGF induces transition from quiescent blood vessels to pathological leaky angiogenesis in wet AMD by studying the fundamental roles of VEGFR2 trafficking. Angiogenesis is restrained in quiescent healthy endothelial cells (ECs), where VEGFR2 trafficking is limited by the interaction with VE-cadherin at adherens junctions (AJs). In contrast, marked VEGFR2 trafficking is evident in angiogenic ECs, where VEGFR2 translocates to filopodia tips that extend towards the VEGF ligand. We provided the first evidence that VEGFR2 is directly transported by the kinesin-3 family protein, KIF13B, a microtubules plus-end motor, to filopodia of sprouting ECs. Based on our finding, we will test our central hypothesis that KIF13B mediates VEGFR2 trafficking away from AJs to induce AJ disassembly and vascular leakage, and the directional trafficking of VEGFR2 to filopodia induces pathological angiogenesis in response to excessive VEGF in wet AMD. Our Specific Aims will test the following hypotheses; 1) KIF13B-mediated VEGFR2 trafficking from AJs breaks the critical interaction between VEGFR2 and VE-cadherin involved in stabilizing AJs, thus induces AJ disassembly and vascular leakage. 2) VEGF signaling induces KIF13B-mediated directional trafficking of VEGFR2 to filopodia extending toward VEGF, and the trafficking is required for sprouting angiogenesis. 3) KIF13B-mediated VEGFR2 trafficking is pathogenesis in wet AMD, thus the inhibition of the trafficking is a promising strategy for the therapy of wet AMD. To rigorously test these hypotheses, our lab has generated powerful tools (genetic mouse models and peptide inhibitors) that have led to conceptual advances. EC specific KIF13B knockout mice display a selective angiogenic defect in the pathological setting. A small peptide inhibitor disrupting the KIF13B/VEGFR2 interaction, termed KAI, inhibited choroidal neovascularization (CNV) in wet AMD model in mice. Using these powerful tools, we will examine the roles of KIF13B in VEGF-induced permeability of ocular blood vessels, live imaging of directional VEGFR2 trafficking in choroidal sprouting ex vivo, and pathology of wet AMD, characterized by abnormal angiogenesis, vascular leakage, and inflammation, using laser-induced CNV model. If successful, our proposed studies provide the novel concept of angiogenesis regulation by targeting VEGFR2 trafficking.